David Allen Brutsche, an adherent of the anti-government sovereign citizen movement, was sentenced to five years probation in Las Vegas in April 2014 after plotting to kidnap and execute a police officer. (AP Photo/Las Vegas Sun/Leila Navidi)

The massacre in June of nine African-American worshippers at the historically black Emanuel AME Church in Charleston, S.C., was the most lethal in a string of ideologically motivated post-9/11 attacks committed by far-right extremists. They range from white supremacists and anti-government militia members to so-called sovereign citizens, who deny the legitimacy of most U.S. laws. Dylann Roof, the 21-year-old suspect in the Charleston killings, is believed to have written an online manifesto ranting against blacks and Hispanics and explaining how a white supremacist website inspired him to commit violence. While experts say most adherents of extremist movements are not violent, a recent survey found that police agencies are more concerned about violence by anti-government extremists than by Islamic extremists. The threat of violence has spurred debate about the strength of the government's efforts to fight extremism and whether it should try to prevent far-right radicalization of young people. Meanwhile, Life After Hate, a group founded by former racist skinheads, is working to help former white supremacists find a new path in life.